The overall goal of the program is to evaluate in a pilot study in HIV-seronegative adults a recombinant anthrax toxin vaccine encoding HIV-1 gag p24 and nef p27 (Therapore-NG). Anthrax lethal toxin is a binary toxin composed of a pore forming protein, protective antigen (PA), and an enzymatic toxin, lethal factor (LF). LF binds specifically to the pore created by polymerized PA, which targets it to the cytosol. These 2 proteins have been engineered to deliver whole proteins for antigen presentation by the MHC class I pathway. The enzymatic toxin portion of LF has been removed and replaced by HIV gag and nef antigens. This vaccine is being developed as one component of an HIV vaccine to induce HIV-specific CD4 and CD8 T cells and is not designed to elicit HIV-specific neutralizing antibodies. If this approach proves safe and elicits HIV-specific cell mediated immunity, it would eventually be tested in combination with other candidate vaccines designed to elicit neutralizing antibodies. Project 1 will complete preclinical animal toxicology studies and produce and perform QA/QC testing on clinical grade Therapore-NG and PA. It is uncertain how best to evaluate vaccine-induced T cell responses, since no vaccine in clinical use was developed for its ability to induce T cell immunity. One of the goals of this program, undertaken by Project 2, is to determine optimal ways to test specific T cell induction in a vaccine setting and develop alternate assays to assess the development of specific T cell responses. The sensitivity, reproducibility, and correlation of new assays will be compared with 51Cr release, lymphoproliferation and ELISPOT assays. Assays will be developed using samples from HIV-infected donors and normal donors vaccinated against smallpox. Sensitivity will be rigorously determined by testing limiting dilutions of antigen-specific T cell clones. Therapore-NG will be tested for clinical safety by Project 3 at the Fenway Community Health Center in a dose escalation pilot study in HIV-seronegative low- risk adults. This study will determine whether Therapore-NG given without adjuvant induces specific CD8 CTL, TH1 or TH2 CD4 T cell responses and/or antibodies. It will also assess the optimal dose for CTL induction and how dose affects the maintenance of specific CTL memory. The ability to use the assays developed in Project 2 in a clinical setting will be tested using the clinical study samples. An Administrative Core will assist in preparing documentation to meet all regulatory guidelines and in study design and statistical analysis and will oversee the fiscal administration of the program. The Immunology Assay Core will perform the assays for induction of antigen- specific T cells and antibodies in the study subjects.